Cement retarder is a kind of retarder that can delay the hydration reaction of cement, thereby prolonging the setting time of concrete, making fresh concrete maintain plasticity for a long time, facilitating pouring, improving construction efficiency, and at the same time, it will not cause adverse effects on various properties of concrete in the later stage. of additives. Lignosulfonate and its derivatives, low molecular weight cellulose and its derivatives, hydroxycarboxylic acid (salt), organic phosphonic acid (salt), boric acid (salt), complexes, etc.